Case Study: nZEC - Energy refurbishment of 5 dwellings in Zwaluwlaan, Wachtebeke, Belgium

Short Description

The main goal was to evaluate the technical and financial feasibility for a social housing company to transform the existing stock into a very energy efficient housing park. The standard procurement procedure was followed.

An architect was selected to do the design, and a market request was published in order to select a contractor. Extra funding was foreseen to cover the extra costs. A follow-up phase is foreseen, with monitoring and education of the inhabitants on how to live in the houses.

Why was the building selected for renovation? The buildings needed to be renovated anyway. The orientation of the selected 5 row houses was ‘ideal’: north-south.

Key Elements

Certification

Annual heating demand  according to passive house standard:

• Dwelling 1: 15 kWh/m²a
• Dwelling 2: 13 kWh/m²a
• Dwelling 3: 13 kWh/m²a
• Dwelling 4: 13 kWh/m²a
• Dwelling 5: 15 kWh/m²a
  
  
  

Thermal Insulation

Floor:

• EPS beads: 45 à 60 cm - λ: 0,036W/mK
• PUR-insulation: 4cm - λ: 0,021W/mK

Walls:

• Polystreen: 34cm - λ: 0,036W/mK
• XPS: 30cm - λ: 0,038W/mK

Roof:

• Rockwool: 24cm - λ: 0,037W/mK
  
  
  

Air Tightness

The airtightness of the project is to be reached by (renewal of) the interior plaster and airtight foils.

Air pressure testing (n50):

• Dwelling 1: 0,56 1/h
• Dwelling 2: 0,53 1/h
• Dwelling 3: 0,59 1/h
• Dwelling 4: 0,59 1/h
• Dwelling 5: 0,55 1/h
  
  
  

Windows and Shading

Thermally insulated window frame with triple glazing:

• Profile 0,80 W/m²K
• Glazing 0,56 W/m²K

External shading devices at the south side.

Ventilation

• Each house has its own ventilation system (Viessman compact Vitotres 343) with heat recovery and an integrated heat pump in combination with solar collectors.
• Controled mechanical ventilation with high efficiency heat recovery.
• Heating via heat pump that uses the heat from the extracted air and converts it to heating energy.
• Extra heating for bathroom.
  
  
  

Heating and Hot Water

• Heating: ventilation + solar gains are maximized in winter by the orientation and size of the windows.
• Hot water is produced with solar collectors in combination with the heat pump.
• The energy consumption and temperature are monitored in function of the external temperature.
  
  
  

Solar Thermal

Each house has its own ventilation system with heat recovery and an integrated heat pump in combination with solar collectors.

Cooling

The solar gains are avoided in summer. It happens by a fixed solar screen above the windows facing the South.

Water Saving

Rain water recovery.

Funding

Total building costs (excl vat):                             

• Vmsw max cost standard (‘regular project’) = 517.724€ (100%)
• Total building cost passive house project = 834.389€  (161%)
• Grant = 170.257€
• Total cost - grant = 664.132€ (128%)
  
  
  

Main Results

• The main goal was to evaluate the technical and financial feasibility for a social housing company to transform the existing stock into a very energy efficient housing park.
• Certified passive houses are – at the moment - too expensive for social housing. As the yearly total budget for new buildings and renovation is limited, the number of new dwellings will be less if the passive house standard is imposed, while there is an urgent need for more social dwellings.
  
  
  

Lessons learned

• A good preparation is key. Working with a building team from the start is a necessity.
• Designers and contractors, but also the client lacks some know how for an optimal realization process.
• Most of the bottlenecks in this project were specific for renovation and not specific for renovation to passivhouse standard: the condition of the existing dwellings was very poor.
• The additional costs to renovate to passive house standards were related to the higher degree of insulation, the difficulties to reach the  air tightness and the existence of thermal bridges.
  
  
  

Additional Information

Mr Bernard Wallyn
VMSW - The Flemish Agency for Social Housing
E-mail: bernard.wallyn@vmsw.be
Web: www.vmsw.be